Fix checking return value of fread()
Merge pull request #1501 from iij/pr_fix_read_debug_section

Fix checking return value of fread()
fix syntax error on Heredoc in expression expansion
but behavior differs from CRuby
Merge branch 'heredoc-in-heredoc-1' of github.com:FUKUZAWA-Tadashi/mruby into heredoc-in-heredoc-1